1. Field of Invention
The present invention relates to a method for fabricating a semiconductor device. More particularly, the present invention relates to a method of protecting a corrosion of tungsten plug.
2. Description of Related Art
In general, after forming a tungsten plug, a wire is formed to couple with the tungsten plug. While performing an etching process to pattern the wire, polymer is formed on sides of the wire. A wet cleaning process is then performed with a stripping solution to remove the polymer.
FIG. 1 is a schematic, cross-sectional diagram illustrating a situation where a wire is aligned over a tungsten plug.
Referring to FIG. 1, a tungsten plug 120 is formed in a substrate 100, and a barrier layer 110 is formed between the substrate 100 and the tungsten plug 120. A patterned wire 130 is formed on the substrate 100. Normally, the wire 130 is aligned over the tungsten plug 120 and covers the entire tungsten plug 120. The wire 130 protects the tungsten plug 120 from corroding while the wet cleaning process is performed with the stripping solution to remove the polymer on the sides of the tungsten plug 120.
FIG. 2 is a schematic, cross-sectional diagram illustrating a situation where a wire is misaligned with a tungsten plug.
Referring to FIG. 2, a portion of the tungsten plug 120 is exposed when the wire 130 is misaligned over the tungsten plug 120. While the wet cleaning process is performed with a stripping solution to remove the polymer on the sides of the tungsten plug 120, the tungsten plug 120 is corroded by the stripping solution and a hole 140 is formed in the tungsten plug 120.
The occurrence of tungsten corrosion is caused by charges accumulated on the wire. While performing the etching process to form the wire 130, the charges are accumulated on the wire 130; thus, a great electrical potential is generated between the tungsten plug 120 and the wire 130. As a result, the exposed tungsten is oxidized to an ionic state such as WO.sub.4.sup.-2 by the stripping solution whose pH value is about 10 to about 12 and dissolved into the stripping solution during the wet cleaning process. Therefore, the hole 140 is formed.
In Bothra et al. (IEEE 98 CH36173.36 Annual International Reliability Physics Symposium, 1998. pp. 150-156), a method to avoid the occurrence of tungsten corrosion is provided. The substrate is dipped into a neutral ionic solution such as deionized water for several hours, and then the wet cleaning process is performed. By dipping the substrate into the neutral ionic solution, the charges accumulated on the wire are discharged; thus, the tungsten plug can be protected from corrosion during the wet cleaning process. However, although the tungsten plug is protected, the wire is corroded by being dipped into the neutral ionic solution. Another method is that the charges are discharged by an electron beam. However, an electron beam machine is not generally used in the manufacturing processes.